Sighting instrument for aerial use.



0. MACKENSEN.

SIGHTING INSTRUMENT FOR AERIAL USE.

APPLICATION FILED MAR.24| 1914.

Patented J 11110 22, 1915.

I heights.

UNITD STATES PATENT OFFICE.

or'ro MAoKnNsEN, or JENA, GERMANY, ASSIGNOR TO THE FIRM or CARL ZEISS,or

JENA, GERMANY.

SI EGHTING INSTRUMENT FOR AERIAL USE.

Specification 01 Letters Patent.

Patented J nne 22, 1915.

Application filed March 24, 1914. Serial No. $26,888.

T all whom it may concern Be it known that I, OTTO MACKENSEN, a citizenof the German Empire, residing at Jena, Germany, have invented a new anduseful Sighting Instrument for Aerial Use, of which the following is aspecification.

The invention relates to instruments for determining the angle, by whichthe connecting line of an aerial vessel in motion with an object on theground aimed at has to deviate, at the moment of releasing a projectile,from the vertical, if the projectile is to hit the said object.According to a wellknown method ofdetermining this angle of deviation,the time taken by an object in traversing a certain angle of the fieldof view is ascertained. Heretofore, in order to make the setting of theangle of deviation with the aid-of a scale possible, the said angle ofthe field of view was always made equal, so that, as the size of thisangle, which is equal for all heights, must be so 'chosen that for smallheights of flight the time taken by an object aimed at to traverse thesaid angle is of practical use, the said time becomes disadvantageouslylong for great Now, if, in order to minimize this disadvantage, the sizeof the angle in the field of view, as has been occasionally doneheretofore, be chosen step by step for different heights of flight insuch a manner that suitable times of observation always result, withevery degree of height, for which a special angle of the field of viewis chosen, a special scale must be provided for the setting of the angleof deviation, orwhen the setting of the said angle is efl'ected, afterits size has been obtained from a tabl ea special table must beprovided. I Now an instrument according to the invention makes itpossible to compensate the relative diflerences of the times ofobservation at difi'erent heights in accordance with the requirements ineach case (while avoiding the above named disadvantages when setting theangle of deviation), by a particular angle of the field of view, whichdecreases as the height increases, being, with the help of. a scalemarked in height-values, coiirdinated to each height. When it has beendecided, how the angle of the field of view is to lie with regard to thevertical, with the aid of the following well-known relations of theangle of the field view, the

angle of deflection, the height of flight and the speed of the airvessel to each other the general rule may easily be given, according towhich the graduation of the scale for the setting of the angle of thefield of view and the connection of the said scale with the device forvarying the size of the latter are to be carried out.

For an air vessel flying at the speed at the height H the angle ofdeviation 0:, by

which the connecting line of the vessel and an object aimed at must beinclined to the vertical at the moment of releasing a projectile, isdetermined, if the projectile is to hit the said object and the airresistance be left out of account, by the well-known equation tan. a

with the vertical line, and that one, in which' the said angle extendsfor all heights by the same amount to both sides of the vertical. In theformer ofthese two special cases (2'. e., where for all heights one ofthe sides of the the vertical), if (5 stands for the said angle and t isthe time taken by the object observed to pass through the angle {5, thefollowing equation holds good:

On substituting this value for o in equation 1, the following equationobtained:

tan. a=

Hence, when it is desired to efiect the setting of the angle ofdeviation with the ald of a non-spatial scale, which is only possible,

said angle of the field of view coincides with when not more than twovariable quantities are to be taken into account, the angle of the fieldof view must be dependent on the height of flight, when it is not to be,as herefurther, in an instrument according to the invention the time ofobservation is not to increase with an increasing height of flight,

tofore, the same size for all heights. As,

tan. B Hk is fulfilled, in which 0 and k are constants of the apparatus.

/ 'When, in accordance with the second of the above named specialeases,the angle of the field of view extends for all heights equally far toboth sides of the vertical, the

following equation holds goodz' p 'v- 2 tan. 5 v(4).

If this value be substituted for o in'equa tion 1, the followingequation is obtained:

. p 2 2 tan.

In this case the setting of the angle of deviation can be effected, whenthe angle of 5 the field of view decreases with increasing height, withone and the same scale for all helghts, for instance, when the scaleserving for the setting of the angle of the field of view the equation vI tan. B= K p or the equation those nstruments may be specially men'-tloned, for whlch the constant k is equal to 1 or 5 For 70:1, forinstance, when the former of the two cases obtains,

tan. [3 so that equation (2) may be written C t I;

its connection with the device for varying the size of the angle of thefield of view is so chosen that for equal speeds of flight the time ofobservation is the same for all heights. It may be also emphasized, thatin this case in place of the time of flight or next to it the speed ofthe aerial vessel can be marked on the arrangement showing the durationof observation.

When the constant '7: is chosen equal to 4 p the same case being againtaken as above,

then

' tan. ,8

and equation (3) may be written tan. a=

tan. [3

only a single variable quantity has to be taken into account, on settingthe angle of deviation, so that after ascertaining the time taken by anobject to traverse the angle of the field of view, the angle ofdeviation,

which would be necessary, if the projectile were to fall in vacuo, canbe set to a scale of.

one dimension, which is marked in timevalues. When, however, the airresistance is Taking as a basis for-the graduation of.

to be taken into account, a scale of two dimensions must be provided inthis case as well, which can then be constructed in just the samemanner, as is necessary in all other cases, even when the air resistanceis not taken into account.

The scale for setting the angle 0f deviation can with advantage beformed in sucha manner that a number of lines, the heightlines, are cutby a number of curves, the time-lines, the latter lines being, for anyoptional disposition of the height-lines, the connecting curves of suchpoints on the height-lines as in each case determine forthe heightcorresponding to'the particular height-line the necessary angle of.devlatlon .for one and the same time of observation.

If the air resistance be neglected, the angles of deviation may beeasily ascertained with the aid of the equations given above, and

thetime-curves consequently determined.-

on taking the air resistance into account, however, the angle ofdeviation must be smaller than the one that is required for the fallingof the projectile in 'viwuo, height and time of observation being thesame in both cases, as the air resistance decreases the horizontaldistance traveled by the projectile. This circumstance can easily beallowed for, by marking on the scale, not the time-lines calculated fromthe above formulae, .but such time-lines as are displaced relatively .tothem by an amount,

I which is determined by experiments or' caltraced for each time ofobservation, if the different influences of different states of theweather on the trajectory of the projectile are to be taken intoaccount,

According to the above, instruments according to the invention must haveat least one line of sight, the inclination of which to the vertical isadjustable; this line must then be able to serve both for setting theangle of the field of view and for realizing the angle of deviation.

Among the instruments, that can be fitted to conform to the invention, adiopter device is particularly simple. As an example such a device isdescribed below, which is to be held during use in the hand of theoperator, and further, let the special case be assumed, in which oneside of the angle of the field of view coincides with the vertical andthe constant of the apparatus, is, is s In the annexed drawing: Figure 1is an elevation of an instrument constructed according to the invention.Fig. 2 is a plan view and Fig. 3 a cross-section through the instrument,on the line 33 of Fig. 2.

The frame of the instrument consists of two plates a and (1 which are atright angles to one another. The plate, 0 which is of approximatelytriangular shape, carries at that one of its angles, which is oppositeto the other rectangular plate a a carrier 0 provided with a notch 0. Ascaletable I) is fixed on the plate a Opposite the notch 0 at the sameedge of the triangular plate a but in the plane of the "scaletable I), afore-sight c is disposed in such a manner that the sighting linedetermined by this sighting device is perpendicular to the plate a andgives the vertical line, when the instrument is so held that a circularlevel a fitted to the carrier 0 indicates that the plates a and a arerespectively in horizontal and vertical positions. A second fore-sightd", which together with the notch 0 forms a second sighting device, thesighting line of which may be given a varying inclination to thevertical, is fitted to a slide d, which engages by means of the tonguesd of its side surfaces (1 and d with the grooves b of the scale-table band can be slid on the latter parallel tothe plates a and a Aplate-spring 03 provided on the side surface 6Z8 of the slide (Z pressesthe latter with its side surface d against the scale-table'b andprevents an unintentional displacement of the slide d. An index d, whichprojects beyond the side surface (Z of the slide 0?, permits of theslide being set with respect to a scale f on the plate a each of thegraduations of which scale indicates that position of the slide, inwhich the angle of deviation of the sighting line passing over the notch0 and the fore-sight d" to the vertical is equal to the angle of thefield of view re quired for the height corresponding to the graduation.By means of a second index 03 of the slide d, which moves across thescale-table b, the settings of the latter for i the realization of theangle of deviation-are effected. The starting points of the time.-lines, lying at the edge 6 of the scale-plate b,marked, corresponding tothe number of seconds required to fly through the angle of the field ofview at different speeds, with the numerals 4, 5 25-represent the scale6 of one dimension for setting those angles of deviation of the sightingline from the vertical, which would be necessary for hitting an objecton the ground, aimed at at the moment of releasing a projectile, if

the said projectile were to fall in 'vacuo,

In combination with the straight lines running parallel to the long edgeof the scaletable, the height-lines marked 200, 300 1000, the time-linespermit of that'correc tion of the setting of the sighting line beingeffected, which is necessary for taking into account, that theprojectile falls in an air-filled space; and such an angle of deviationis determined, on setting the index d of the slide d on the point ofintersection of a time-line (e. g., as in the drawing, of the time-linebelonging to 10 seconds) with a height-line (e. g. with the height-huebelonging to 500 m.), thatif the air vessel be traveling at the heightcorresponding to the height-line (in the example 500 m.) at such a speedthat for traversing the angle of the field of view the time correspondmgto the time-line (10 seconds) is requ1redthe object on the ground, aimedat at the moment of releasing the projectile, w1ll be hit.

An instrument, in which the .constant 71 would not have the value 1},but another one, 6. g. the value 1, would need to dlfl'er from theexample shown only by a different graduation of the scale When using theinstrument described, the observer mustto recapitulate the separatemanipulations to be carried out by him first of all set the sightingline in corre- &

spondence' with the ascertained height of flight by the scale 7, anddetermine the time taken by the air vessel to travel from a spot, fromwhich an object on the ground, aimed at, lying in the direction oftravel, appears in the direction of the said sighting line, to a spotlying vertically above the saidobject. Thereupon the index d of theslide (i must be set on the point of intersection of that height-line,the marking of which agrees with the ascertained height of flight, withthe time-line corresponding to the said time.

At the moment, at which the sighting line connecting the notch 0 withthe fore-sight d passes through the object aimed at, the projectile mustbe released.

I claim: I t

In a sighting instrument for aerial use means for sighting in directionsvariably inclined to the vertical, a member bearing graduationsrepresenting height. values, an index connected with the said sightingmeans, the said member andthe said index being adapted for relativemovement, a second member bearing graduations representing height valuesand time values and a, y

second index also connected with the said sighting means, the lattermember and mdex being also adapted for relative movement, which latterrelative movement is dependent on-the relative movement of the firstnamed'member and index;

OTTO MACKENSEN. .Witnesses:

PAUL Km'ienn, FRITZ SANDER. v

